package ch.epfl.maze.physical.zoo;

import ch.epfl.maze.physical.Animal;
import ch.epfl.maze.physical.ProbabilisticAnimal;
import ch.epfl.maze.util.Direction;
import ch.epfl.maze.util.Trail;
import ch.epfl.maze.util.Vector2D;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.stream.Collectors;

/**
 * Panda A.I. that implements Trémeaux's Algorithm.
 *
 * @author Pacien TRAN-GIRARD
 */
public class Panda extends ProbabilisticAnimal {

    private final Trail trail;

    /**
     * Constructs a panda with a starting position.
     *
     * @param position Starting position of the panda in the labyrinth
     */
    public Panda(Vector2D position) {
        super(position);
        this.trail = new Trail();
    }

    /**
     * Checks if the current position is an intersection given the possible choices.
     *
     * @param choices An array of possible Directions
     * @return T(the current position is an intersection)
     */
    private boolean isIntersection(Direction[] choices) {
        return choices.length > 2;
    }

    /**
     * Get the Marking at the adjacent position given the Direction.
     *
     * @param dir The Direction from the current position
     * @return The Marking
     */
    private Trail.Marking getMarkingAtDirection(Direction dir) {
        Vector2D pos = this.getPosition().addDirectionTo(dir);
        return this.trail.getMarking(pos);
    }

    /**
     * Checks if all Direction choices are leading to the given Marking.
     *
     * @param choices An array of possible Directions
     * @param marking The Marking
     * @return T(all choices are leading to positions with the given Marking)
     */
    private boolean allChoicesLeadingTo(Direction[] choices, Trail.Marking marking) {
        return (new ArrayList<>(Arrays.asList(choices)))
                .stream()
                .allMatch(dir -> this.getMarkingAtDirection(dir) == marking);
    }

    /**
     * Selects the Direction choices leading to the given Marking.
     *
     * @param choices An array of possible Directions
     * @param marking The Marking
     * @return An array of choices leading to the given Marking
     */
    private Direction[] selectDirectionsWithMarking(Direction[] choices, Trail.Marking marking) {
        return (new ArrayList<>(Arrays.asList(choices)))
                .stream()
                .filter(dir -> this.getMarkingAtDirection(dir) == marking)
                .collect(Collectors.toList())
                .toArray(new Direction[0]);
    }

    /**
     * Selects the best choices according to the neighbours Markings.
     *
     * @param choices An array of possible Directions
     * @return An array of smart choices
     */
    private Direction[] selectBestDirections(Direction[] choices) {
        // special case
        if (this.isIntersection(choices) && this.allChoicesLeadingTo(choices, Trail.Marking.AVOID_MARKING))
            return new Direction[]{this.currentDirection.reverse()};

        // general case
        for (Trail.Marking mark : Trail.Marking.ALL) {
            Direction[] smartChoices = this.selectDirectionsWithMarking(choices, mark);
            if (smartChoices.length > 0) return smartChoices;
        }

        // panda is trapped :(
        return new Direction[]{};
    }

    /**
     * Determines if the current position should be marked according to the rules of the <i>Trémeaux's Algorithm</i>,
     * avoiding intersections over-marking.
     *
     * @param choices An array of possible Directions
     * @param choice The selected Direction
     * @return T(the current position should be marked)
     */
    private boolean shouldMarkCurrentPosition(Direction[] choices, Direction choice) {
        return !(this.isIntersection(choices)
                && this.trail.getMarking(this.getPosition()) == Trail.Marking.AVOID_MARKING
                && this.getMarkingAtDirection(choice) == Trail.Marking.NO_MARKING);
    }

    /**
     * Marks the current position according to the rules of the <i>Trémeaux's Algorithm</i>.
     *
     * @param choices An array of possible Direction to take
     */
    private void markCurrentPosition(Direction[] choices) {
        if (choices.length == 1 && this.allChoicesLeadingTo(choices, Trail.Marking.AVOID_MARKING)) // dead end
            this.trail.markPosition(this.getPosition(), Trail.Marking.NO_GO_MARKING);
        else
            this.trail.markPosition(this.getPosition());
    }

    /**
     * Moves according to <i>Trémeaux's Algorithm</i>: when the panda
     * moves, it will mark the ground at most two times (with two different
     * colors). It will prefer taking the least marked paths. Special cases
     * have to be handled, especially when the panda is at an intersection.
     */
    @Override
    public Direction move(Direction[] choices) {
        Direction[] smartChoices = this.selectBestDirections(choices);
        Direction choice = super.move(smartChoices);

        if (this.shouldMarkCurrentPosition(choices, choice))
            this.markCurrentPosition(choices);

        return choice;
    }

    @Override
    public Animal copy() {
        return new Panda(this.getPosition());
    }

}